Consumer and commercial appliances, such as for example clothes dryers, typically include some form of program timer that allows the user to select a desired operating cycle. In typical appliances, these program timers are embodied in a motor driven cam stack having a number of control switches that are operated via followers. These followers track one of the control faces on the cam stack. The selection of the particular program cycle is typically made via a rotary switch that is rotated to a particular position based on the graphics on the control panel of the appliance. This mechanical interface to the program timer control is familiar to consumers and provides a very simple user interface. Indeed, such a mechanical knob interface is still used in many electronic controllers that utilize a microprocessor to control the various operating cycles as opposed to the rotating cam stack.
Once the appropriate or desired program cycle is selected by the user, the appliance is started via actuation of a momentary contact switch. Typically, this start switch is a push button switch. Actuation of this momentary contact push button start switch energizes the start windings of the appliance's main motor. Once the motor begins to rotate, a centrifugal switch in the main motor actuates to maintain its energization. The user is then free to release the momentary contact push button start switch.
In one type of conventional appliance, the momentary contact push button start switch is integrated into the program cam stack controller. In such a configuration, the program selector knob is depressed to start the main motor of the appliance. That is, in this type of conventional appliance, the program selector knob is rotated to select a desired program cycle, and is then depressed momentarily to start the selected program cycle.
Unfortunately, such a program timer with an integrated push button start switch is subject to misoperation by the user, resulting in shortened switch life and erroneous program operation. That is, because the momentary contact push button switch is integrated into the rotary control knob of the program timer, a user may inadvertently push in the knob while turning the knob to select a desired program cycle. If the knob is depressed far enough while rotating the knob to select a desired program cycle, the momentary contact push button switch may intermittently make contact. This energizes or attempts to energize the start winding of the appliance motor. This intermittent operation may damage the appliance motor, and may result in intermittent arcing between the switch contacts as they are intermittently connected and disconnected during the rotation of the switch. This arcing may damage and thus shorten the switch life itself.
Even if the momentary contact push button switch is not actuated intermittently during rotation of the program timer control knob, the speed and consistency at which the user presses the control knob to start the appliance may still result in intermittent or otherwise inappropriate contact of the momentary contact push button switch. That is, if the user were to slowly depress the rotary knob the contacts may intermittently make and break contact numerous times before a firm contact is made. This will result in excessive arcing between the switch contacts and will shorten the life of the switch. Likewise, if the user were to withdraw the knob slowly once the appliance had been started, the slow separation of the electrical contacts of the momentary contact push button switch will draw and sustain an electrical arc. This will also serve to damage and thus shorten the life of the program timer.
Recognizing the deficiency with the integrated program controller and start switch, many manufacturers employ an appliance control panel that separates the program timer control selection knob from the start switch. In such appliances, the user first selects the desired program cycle with the rotary program cycle select switch. Once the appropriate cycle has been selected, the user presses a separate momentary contact start switch located on the appliance's control panel. Unfortunately, while separating these two functions eliminates the intermittent starting of the appliance while the user is selecting a desired program cycle, the separate start switch is still subject to damage based on the manner in which the user depresses and releases the switch. That is, the arcing problem described above resulting in shortened life of the switch is still prevalent as the user may slowly depress or slowly release the separate start switch in a manner that results in arcing.
There exists, therefore, a need in the art for a program timer that can perform the appliance start function without the intermittent arcing problems currently existing in the art.